| USB Legacy support |
| ~~~~~~~~~~~~~~~~~~ |
| |
| Vojtech Pavlik <vojtech@suse.cz>, January 2004 |
| |
| |
| Also known as "USB Keyboard" or "USB Mouse support" in the BIOS Setup is a |
| feature that allows one to use the USB mouse and keyboard as if they were |
| their classic PS/2 counterparts. This means one can use an USB keyboard to |
| type in LILO for example. |
| |
| It has several drawbacks, though: |
| |
| 1) On some machines, the emulated PS/2 mouse takes over even when no USB |
| mouse is present and a real PS/2 mouse is present. In that case the extra |
| features (wheel, extra buttons, touchpad mode) of the real PS/2 mouse may |
| not be available. |
| |
| 2) If CONFIG_HIGHMEM64G is enabled, the PS/2 mouse emulation can cause |
| system crashes, because the SMM BIOS is not expecting to be in PAE mode. |
| The Intel E7505 is a typical machine where this happens. |
| |
| 3) If AMD64 64-bit mode is enabled, again system crashes often happen, |
| because the SMM BIOS isn't expecting the CPU to be in 64-bit mode. The |
| BIOS manufacturers only test with Windows, and Windows doesn't do 64-bit |
| yet. |
| |
| Solutions: |
| |
| Problem 1) can be solved by loading the USB drivers prior to loading the |
| PS/2 mouse driver. Since the PS/2 mouse driver is in 2.6 compiled into |
| the kernel unconditionally, this means the USB drivers need to be |
| compiled-in, too. |
| |
| Problem 2) can currently only be solved by either disabling HIGHMEM64G |
| in the kernel config or USB Legacy support in the BIOS. A BIOS update |
| could help, but so far no such update exists. |
| |
| Problem 3) is usually fixed by a BIOS update. Check the board |
| manufacturers web site. If an update is not available, disable USB |
| Legacy support in the BIOS. If this alone doesn't help, try also adding |
| idle=poll on the kernel command line. The BIOS may be entering the SMM |
| on the HLT instruction as well. |
| |
